The present invention concerns printing apparatuses in general, for example, screen printing or graphic arts apparatuses, which typically include printing apparatuses of the endless drive path varieties.
Heretofore, various types of printing devices have been used. In general, several ways of conveying a substrate to a singular printing position, or multiple positions, have been employed, including: an endless printing blanket traveling horizontally with an upper print surface and a lower return flight; an endless chain having pallets attached which travel along a circular path with upper and lower return levels; an endless chain with pallets attachments traveling in an oval configuration on a single horizontal plane; and a series of platens attached to a central rotatable hub from which pallets and screens extend outward to a circular circumference, wherein the screens and pallets travel on a horizontal plane following the pathway determined by the circumference of the circle.
Thus, one example of a known screen printing device drives a plurality of supported pallets around an endless path, wherein the pallets are indexed to desired printing stations, for example where a printing head may be located, so as to impart a screened pattern of ink from the printing head onto a substrate, such as an article of clothing. Various patterns or colors may be disposed onto the clothing during its journey through the endless path. Such known devices are described in the following patents, all of which are incorporated herein as if fully set out in their entirety: U.S. Pat. No. Re. 29,160 issued to Jaffa; U.S. Pat. No. 4,407,195 issued to Jaffa; and U.S. Pat. No. 5,456,172 issued to Herrmann. The path of the pallets on these oval track machines thus comprises two parallel straight sections and two arcuate end sections. In order to provide an increased number of printing stations, the length of the parallel straight sections must be increased. Consequently, sufficient factory floor space must be provided which can accommodate the boundaries of such a machine. That is, a substantially elongated rectangular block of floor space must be available in order to increase the printing capacity provided by such machines. Furthermore, the arcuate end sections of the path are typically not utilized for printing, as the pallets experience considerable centrifugal acceleration as they are whipped around these sections as necessitated by a desired production speed of the pallets which generates an acceptable number of printed material at an acceptable rate. Consequently, the connections between the pallets and the means for driving the pallets around the endless path suffer various stresses, leading to increased maintenance costs. One approach to the problem of high stresses on these connections provided resilient mounts for absorbing some of the undesirable forces.
Another type of known printing device is the round or rotary screen printing device. For example, a plurality of screens may be mounted coaxially with a plurality of workpiece supporting pallets such that the transfer of ink through the screens to the workpieces is achieved by rotation about a single upright axis. Such known devices are described in the following patents, all of which are incorporated herein as if fully set out in their entirety: U.S. Pat. No. 4,606,268 issued to Jaffa; and U.S. Pat. No. 5,438,922 issued to Bubley et al. Such devices require rotation of a large assembly about a single axis, requiring large torques, and resulting in high drive requirements and high maintenance costs due to wear. Furthermore, these devices require a considerable block of floor space. For example, a certain minimum size rotary machine is required to accommodate a minimum number of pallets, since the pallets, or the desired printing surfaces, typically require a minimum printing area width. When the inner ends of a plurality of typical rectangular shaped pallets are spaced around a circle, a minimum diameter circle is defined for a given number of pallets. In other words, the rear ends of the pallets converge. If it is desired to increase the number of pallets, the circle must be widened. Thus, the overall size and diameter of such machines increases rapidly as the number of pallets which the device can accommodate is increased, thereby increasing loads and stresses on the machine, and thereby increasing the demand for a large block of factory space. Furthermore, registration becomes more difficult as the circumference becomes larger.
Various other known screen printing apparatuses and subsystems therefor already exist. For example, the following patents, all of which are incorporated as if fully set out herein, describe various screen printing devices: U.S. Pat. Nos. 4,031,825; 4,735,139; 4,846,058; 4,909,146; 4,938,130; 5,483,882; and 5,607,243.
Thus, known devices are limited in flexibility to efficiently and effectively accommodate various numbers of pallets or printing stations, and further do not provide flexibility with respect to factory floor plan constraints.
As used herein, "pallet" generally refers to a workpiece support which is driven along a path so as to place a workpiece into a desired printing location with respect to a printing head. Thus, a pallet may refer to a member which is attached to a pallet drive means and which may be elsewhere be variously referred to as a "pallet support" or the like. Additionally, as used herein, the term "pallet" may also comprise another member which is attached to such a support or base support, wherein such other member may be adapted to further hold the workpiece in a desired manner, and which may be referred to by a skilled artisan as a pallet. Thus, as used herein, the term "pallet" is intended to broadly encompass a pallet means, or a pallet assembly, which may include a pallet support and an additional member which further supports the workpiece disposed thereon.
As used herein, "polygonal" generally refers to the configuration or shape derived from a polygon, i.e. a closed plane figure bounded by three or more line segments The term "polygonal" is intended to broadly encompass a wide variety of shapes, including regular and irregular formations.